Development and Characterization of Corrosion Resistant Coatings Using the Natural Biopolymer Chitosan

In the present study, chitosan, a derivative of naturally abundant biopolymer chitin, was used as the basis for corrosion resistant coating. Chitosan suffers from two inherent weaknesses as a coating material namely its high hydrophilicity and its poor adhesive strength with Al 2024 T3 alloy. In the present study, chitosan structure was modified using epoxy functional silane and vanadate. Performance of different coatings was tested using electrochemical impedance spectroscopy, adhesion testing and salt spray testing. The best salt spray performance was observed in case of chitosan-(3-Glycidoxypropyl)-trimethoxysilanevanadate coatings, which lasted 450 hours in salt spray chamber without visible corrosion. UV/Visible spectroscopy measurements showed release of vanadate by chitosan increases with increasing solution pH. This property of chitosan provides self-healing characteristics to these coatings. When the solution pH is readjusted to a lower value, chitosan can readsorb released vanadate. FTIR spectra of chitosan gel showed adsorption of vanadate at protonated amine sites. Chitosan showed a maximum in the vanadate adsorption capacity in the pH 3 to 5 range.